The objective of this exploratory study is to examine the utility of high resolution computed tomography (HRCT) to measure changes in functional pulmonary imaging parameters as a function of short term a) iNO administration and b) nitric oxide (NO) cylinder concentration using the investigational medical device INOpulse® DS-C in subjects with WHO Group 3 PH associated with COPD on LTOT (Part 1) and in Subjects with WHO Group 3 PH associated with Idiopathic Pulmonary Fibrosis (IPF) on LTOT (Part 2 and Part 3)